For certain construction projects, elongate members such as piles, anchor members, caissons, and mandrels for inserting wick drain material must be placed into the earth. It is well-known that such rigid members may often be driven into the earth without prior excavation. The term “piles” will be used herein to refer to the elongate rigid members typically driven into the earth.
One system for driving piles is conventionally referred to as a diesel hammer. A diesel hammer employs a floating ram member that acts both as a ram for driving the pile and as a piston for compressing diesel fuel. Diesel fuel is injected into a combustion chamber below the ram member as the ram member drops. The dropping ram member engages a helmet member that transfers the load of the ram member to the pile to drive the pile. At the same time, the diesel fuel ignites, forcing the ram member and the helmet member in opposite directions. The helmet member further drives the pile, while the ram member begins a new combustion cycle. Another such system is a drop hammer that repeatedly lifts and drops a hammer onto an upper end of the pile to drive the pile into the earth.
Diesel hammers seem to exhibit fewer problems with tension cracking in concrete piles and pile driving helmets than similarly configured external combustion hammers. The Applicant has recognized that the combustion chambers of diesel hammers pre-load the system before the hammer impact and that this preloading may explain the reduction of tension cracking in concrete piles associated with diesel hammers.
The need thus exists for improved drop hammers that induce stresses in the pile driven that are similar to the stresses induced by diesel hammers.